Genetic structure of disjunct Argentinean populations of the subtropical tree Anadenanthera colubrina var. cebil (Fabaceae)

Abstract

Anadenanthera colubrina var. cebil is a native South American tree species inhabiting seasonally dry tropical forests (SDTFs). Its current disjunct distribution presumably represents fragments of a historical much larger area of this forest type, which has also been highly impacted by human activities. In this way the hypothesis of this study is that the natural populations of A. colubrina var. cebil from Northern Argentina represent vestiges of ancient fragmentation, but they are additionally influenced by a certain degree of gene flow among them. We aimed to analyze the genetic structure of both nuclear and chloroplast DNA to evaluate the relative role of ancient and recent fragmentation on intraspecific diversity patterns. Sixty-nine individuals of four natural populations were analyzed using eight nuclear microsatellites (ncSSR) and four chloroplast microsatellite loci (cpSSR). The level and distribution of genetic variation were estimated by standard population genetic parameters and Neighbor Joining as well as Bayesian analyses. The eight ncSSR loci were highly polymorphic, while genetic diversity of cpSSRs was low. Nuclear SSRs displayed lower genetic differentiation among populations than cpSSR haplotypes (F ST 0.11 and 0.95, respectively). However, high differentiation between phytogeographic provinces was observed in both genomes. The high genetic differentiation detected emphasizes the role of ancient fragmentation. However, the Paranaense province also shows the effects of recent fragmentation on genetic structure, whereas gene flow by pollen preserves the effects of genetic drift in the Yungas province.

Back to the future: Evidence of ancestral polymorphism in current populations of Anadenanthera colubrina var. cebil by means of Population Graphs

“…cebil (Barrandeguy et al, 2014). This result was unexpected for nuclear genome because of high mutation and recombination rates of nuclear microsatellites (nuSSRs), as well as the high levels of gene flow by pollen that can erase the genetic differences (Barrandeguy et al, 2014). However, this previous work did not develop an analysis to test this conclusion for the nuclear genome.…”

“…In a previous study, historical fragmentation was proposed as possible explanation for nuclear and chloroplast genetic structure detected in natural populations of A. colubrina var. cebil (Barrandeguy et al, 2014). This result was unexpected for nuclear genome because of high mutation and recombination rates of nuclear microsatellites (nuSSRs), as well as the high levels of gene flow by pollen that can erase the genetic differences (Barrandeguy et al, 2014).…”

“…Sampled populations from the North of Argentina were Candelaria and Santa Ana from Paranaense phytogeographic province and Tucumán and Jujuy from Yungas phytogeographic province. Eight nuclear microsatellite loci were analyzed and the methodology is described in Barrandeguy et al (2014) (Fig. 1).…”

Demografía histórica de Anadenanthera colubrina var. cebil (Leguminosae) en Argentina.

“…El movimiento de las semillas constituye el componente más importante de la dinámica de las poblaciones vegetales, ya que la regeneración y la colonización de hábitats requieren del movimiento de la información genética a través de las semillas (Finkeldey & Hattemer, 2007). En este sentido, Barrandeguy et al (2014), estudiando cuatro poblaciones de A. colubrina var. cebil determinaron moderada estructuración genética poblacional a nivel del genoma nuclear (cuya dispersión ocurre tanto por polen como por semillas) mientras que determinaron elevada estructuración genética a nivel del genoma cloroplástico e interpretaron estos resultados como consecuencia de fragmentación histórica.…”

“…Se identificó taxonómicamente a los especímenes colectados por medio de los tratamientos disponibles para el género (Altschul, 1964;Cialdella, 2000;Martínez et al, 2013). Se colectaron hojas jóvenes de individuos adultos siguiendo la metodología descripta en Barrandeguy et al (2014). Los individuos fueron georreferenciados mediante el sistema de posicionamiento global (GPS).…”